Single-story steel buildings such as car parks and industrial halls are often characterised by stiff beams and flexible columns and may experience an outward (sway) collapse during a fire, endangering people and properties outside the building. It is therefore a current interest of the research to investigate the collapse behaviour of single-story steel frames and identify relevant structural characteristics that influence the collapse mode. In this paper, a parametric study on the collapse a steel beam-column assembly with beam hinged connection and fixed column support is carried out under the assumption of a protected column and a standard temperature-time curve on the beam. The study shows that sway collapse can be avoided by increasing either the restrain offered by the column or the load-to-resistance ratio of the beam. It seems possible to extend these results to multi-span frames with bracing system, in case of a fire located on one outer span –situation that represents the worst case for the risk of sway collapse. With respect to this type of frames, a methodology is proposed for the development of design tables that relate the profiles of the elements to the soliciting load on the beam. By means of those tables, a simple method for the assessment and the countermeasure of unsafe collapse mode of single-story steel buildings can be derived.